Imaging Bioturbation in Supratidal Carbonates: Non-Invasive Field Techniques Enhance Neoichnological and Zoogeomorphological Research, San Salvador, The Bahamas
A case study in unconsolidated carbonates on San Salvador Island, The Bahamas, utilized high-frequency (800 MHz) georadar imaging to augment existing methodologies (burrow counts and measurements, casting) in brachyuran bioturbation research (Ocypode quadrata and Gecarcinus lateralis), and as part of a new dataset characterizing blue land crab (Cardisoma guanhumi) burrows. Non-invasive techniques such as ground-penetrating radar (GPR) can complement traditional field surveys aimed at quantifying mesoscale bioturbation in modern settings. These methods can establish diagnostic features for tracemaker identification and refine existing ichnofacies models. Drone-mounted aerial coverage provided the first high-resolution images of the micro-topography and large burrow openings of Cardisoma in supratidal muddy sands. Measurements of 20 burrows (minimum length, entrance diameter, and spoil mound size) were complemented by endoscopic camera observations (burrow fill, large bioglyphs, and occupants). Extensive 2D transects and quasi-3D georadar grids not only reveal characteristic subsurface interfaces (open vs. filled burrow, water table, saltwater), but also serve as an archive of bulk in situ sedimentary characteristics of the bioturbated substrate. Signal resolution in dry carbonate sand (~ 4 cm) was sufficient to differentiate and measure known burrow structures. Our study demonstrates that co-located and georeferenced aerial, geophysical, and ground-based databases will allow rapid and effective assessment of the spatial distribution and gross geometry of comparable biogenic structures in a variety of environments and substrates
